The invention generally relates to a method for removing or eliminating carbon dioxide from waste gases. More specifically, the present invention is a method for removing or eliminating carbon dioxide from waste gases by contacting the waste gases with an absorbent composition. The absorbent composition absorbs the waste gases which thereby eliminates the carbon dioxide from the waste gases.
In recent years, a greenhouse effect by carbon dioxide is indicated as one cause of the warming phenomenon of the earth, and its prompt resolution is globally required in order to protect earth circumstances. The generation sources of carbon dioxide extend in active fields of all humans in which fossil fuels are burned, and there is a tendency that the discharge regulation of carbon dioxide will be further tightened in the future. Thus, for power generation facilities such as power plants in which a large amount of the fossil fuel is used, there are energetically researched a method for removing and recovering carbon dioxide from a combustion exhaust gas.
Purification of process gas streams by the removal of acid gases such as carbon dioxide is required in many major industrial processes such as hydrogen manufacture for refinery hydrotreating, synthesis gas manufacture from coal, purification of natural gas, and ammonia manufacture. Also, the purification of gas streams from automobile combustion gases is also a major concern for auto manufacturers. Bulk removal of acid gases from such streams is usually accomplished by use of a scrubbing solution composed of a solvent.
As disclosed below, there are many patents that discuss how to separate an acidic gas, such as carbon dioxide, from a gas stream. Japanese Patent Application Laid-open No. 100180/1978 discloses a method for removing an acidic gas which comprises bringing a usually gaseous mixture into contact with an amine-solvent liquid absorbent comprising (1) an amine mixture comprising at least 50 mole % of a steric hindrance amine constituting a part of a ring and having at least one secondary amino group bonded to either of a secondary carbon atom or a tertiary carbon atom or a primary amino group bonded to the tertiary carbon atom, and at least about 10 mole % of the tertiary amino-alcohol, and (2) a solvent for the above-mentioned amine mixture which functions as a physical absorbent for the acidic gas. Usable examples of the steric hindrance amine include 2-piperidine ethanol[2-(2-hydroxyethyl)-piperidine] and 3-amino-3-methyl-1-butanol, and a usable example of the tertiary amino-alcohol is 3-dimethylamino-1-propanol. Furthermore, an example of the solvent is a sulfoxide compound which may contain water in an amount of 25% by weight or less, and an example of a gas to be treated is “a usually gaseous mixture containing carbon dioxide and hydrogen sulfide at high concentrations, for example, 35% of Carbon dioxide and 10-12% of H.sub.2 S” on page 1, left upper column of the same gazette. In the undermentioned examples, Carbon dioxide itself is used.
In Japanese Patent Application Laid-open No. 71819/1986, there is described a composition for the scraping of an acidic gas which contains a non-aqueous solvent such as a steric hindrance amine or sulfolane. As an example of the primary monoamino alcohol of the steric hindrance, 2-amino-2-methyl-1-propanol (abbreviated to AMP) is exemplified and used. In examples, Carbon dioxide and nitrogen as well as Carbon dioxide and helium are used. Furthermore, as absorbents, an aqueous solution of an amine and potassium carbonate, and the like are used. The use of water is also referred to. In addition, this gazette describes the advantage of the steric hindrance amine in the absorption of carbon dioxide by reaction formulae.
In Chemical Engineering Science, Vol. 41, No. 4, pp. 997-1,003, there is disclosed a carbon dioxide gas absorption behavior of an aqueous AMP solution which is a hindered amine. As gases to be absorbed, carbon dioxide and a mixture of carbon dioxide and nitrogen at atmospheric pressure are used.
U.S. Pat. No. 3,622,267 discloses a technique in which an aqueous mixture containing methyldiethanolamine and monoethylmonoethanolamine is used to purify a high-partial pressure carbon dioxide contained in a synthetic gas such as a partially oxidized gas of a crude oil or the like, for example, a synthetic gas containing 30% of Carbon dioxide at 40 atm.
Consequently, there is a need for an absorbent composition capable of absorbing carbon dioxide from waste gases in a more efficient manner.